3B Scientific Bolometer User Manual
Page 4
Elwe Didactic GmbH • Steinfelsstr. 6 • 08248 Klingenthal • Germany • www.elwedidactic.com
3B Scientific GmbH • Rudorffweg 8 • 21031 Hamburg • Germany • www.3bscientific.com
Subject to technical amendments
© Copyright 2008 3B Scientific GmbH
•
Set up the bolometer as shown in Figure 1, using
the stand, rod and clamps.
•
Adjust the bolometer so that the sunlight shines
exactly along its axis. The shadow of the front
end-plate should then fall exactly onto the rear
end-plate.
•
Before inserting the thermometer into the hole
in the aluminium cylinder, put in a few drops of
water to improve the transfer of heat.
•
Insert the thermometer into the hole, read the
initial temperature, and record it in a table.
•
In a series of measurements over a period of 10
minutes, read the temperature at intervals of 60
seconds and record the values.
•
Remove the rear end-plate, unscrew the
aluminium cylinder, and determine its mass m
by weighing.
•
Using the callipers, measure the diameter d of
the blackened surface and calculate the area A.
•
Plot a graph of temperature against time to
show the heating-up of the aluminium cylinder.
Draw a line of best fit through the data points.
The temperature rise per minute,
ΔT, is obtained
from the gradient of the line.
The quantity of heat Q received by the blackened
surface of the aluminium cylinder in one minute can
be calculated from the temperature rise per minute
ΔT, the mass m of the cylinder, and the specific heat
capacity of aluminium
Al
c
:
T
m
c
Q
Al
Δ
⋅
⋅
=
(1)
The specific heat capacity of aluminium is
C
kg
J
896
c
Al
°
⋅
=
.
•
Using Equation 2, calculate the radiation power
per unit area (heat input per cm
2
per minute).
A
Q
S
=
(2)
3.2 Measuring the radiation power of a filament
lamp
Additional equipment needed:
1 E14 lamp socket
U8495320
1 Filament lamp 12 V, 25 W, type E14 as sold for
domestic use
1 Transformer with rectifier (230 V, 50/60 Hz)
U33300-230
or
1 Transformer with rectifier (115 V, 50/60 Hz)
U33300-115
Experiment leads
Air is a poor conductor of heat, and therefore
thermal conduction makes only a very small
contribution in this experiment. Furthermore, as the
heated air near the lamp flows upward and not
towards the “black body”, thermal convection also
makes no significant contribution to the heating of
the aluminium cylinder.
•
Screw the filament lamp into the lamp socket
and connect to the power supply.
•
Remove the cardboard tube and support the
aluminium cylinder with one end-plate using a
stand and clamp (Fig. 2).
•
Position the aluminium cylinder so that its
distance l from the lamp filament is about 4 cm.
•
Determine the quantity of heat per minute and
the radiation power per unit area in the same
way as in Experiment 3.1.
If the lamp filament is regarded as a point source of
radiation, the total radiation power S
G
that is emitted
by the lamp is the amount received by a sphere of
radius r = l. Therefore it is the product of the
calculated radiation power per unit area, S, and the
surface area of the sphere A
O
:
S
A
S
G
⋅
=
0
°C
Fig. 1 Measuring the radiation power of the sun
°C
Fig. 2 Measuring the radiation power of a filament lamp